In a field of railway, as safety systems for preventing a collision between trains, signal systems such as an ATS (automatic train stop system) and ATC (automatic train control system) have been introduced. For example, in a single-stage brake ATC system (referred to as a “single-stage ATC” from now on), information called an ATC telegram is transmitted from the ground to a train via rails. An enterable limit track circuit (referred to as a “stop track circuit” from now on) for the following train is decided by an occupied track circuit of the preceding train, and the track circuit ID thereof is contained in an ATC telegram and is transmitted to the following train. The ATC telegram is transmitted on a track circuit basis, and includes the track circuit ID of its own, that is, the ID of the track circuit where the current train is present now. The following train calculates the remaining distance to be covered to a stopping position according to the stop track circuit ID and creates brake pattern. The train has a mechanism of considering the brake pattern as a speed limit and of braking automatically when exceeding the speed limit.
A multistage ATC system (referred to as a “multistage ATC” from now on), on the other hand, has a mechanism of transmitting speed limit information called ATC aspect via rails, and of braking automatically if the speed of the current train exceeds the speed limit indicated by the ATC aspect. Here, the ATC aspect is decided on the ground side according to a combination of the occupied track circuits of the preceding train and the current train.
A driver controls the train within the speed limit given by the ATC. In some routes, an ATO (automatic train operation system) has been introduced which controls the train automatically from a station departure to station arrival. The ATO also controls the train automatically within the speed limit given by the ATC in the same manner as the operation by a driver. To the driver or ATO, a scheduled train performance curve which indicates relationships of the position between stations and the speed is given as a reference of running. The scheduled train performance curve is designed in such a manner as to enable the train to run on schedule when moving according to it.
Normally, a train is seldom affected by the speed limit of the preceding train, and it can run on a scheduled train performance curve. However, if the train schedule is disrupted, the distance from the preceding train can reduce. Accordingly, the speed limit is altered to a lower level than the scheduled train performance curve by the ATC, and the train cannot run on the scheduled train performance curve, and sometimes has to stop temporarily between stations in a bad case. In this case, the train cannot arrive at the next station on schedule. In addition, there is a problem of increasing power consumption and deteriorating ride quality because of extra acceleration and deceleration.
Such a problem is apt to occur when the preceding train is stopped at a station and its departure is behind schedule and when the following train is moving toward the station. This is because the distance between the two trains is apt to be shortened by the amount of being stopped at the station, and the speed limit is reduced by that amount.
In normal times, if the following train retains the train timetable information about the preceding train, it can estimate the time when the preceding train will leave the station and adjust its speed according to the time. However, in conditions where the train timetable is disrupted, the train timetable information it retains in advance is useless.
As a method of solving the problem, a technique is proposed which estimates the station departure time of the preceding train on the ground side and notifies the following train of the optimum approaching speed (see Patent Document 1, for example). Here, the optimum approaching speed to be notified is the speed calculated in such a manner that enables the following train to avoid a temporary stop and that makes the time interval between departure and arrival shortest. It tries to improve the riding quality and power consumption by avoiding the temporary stop due to a speed limit by decelerating from an early stage and running slowly, and thus to prevent the train schedule from being increasingly disrupted. In addition, a technique is proposed which detects opening and shutting time of doors on the ground side and notifies the following train of that result so that the following train reduces its running speed automatically (see Patent Document 2, for example).